You will need wheel 50 to 80 grit to keep it spherical and drive it concave, the brand is unimportant, just the grit size. Coarser diamond will work too and go faster but will take longer to clean up subsurface damage. However a 1/2 diameter wheel will remove some glass at the edge which you don't want if your blank is already thin or to save center thickness. So in my video I ran one or two smaller wheels 1/4 and 1/8 diam. for maybe 3 minutes to remove glass at the center. I then mark this area with a pencil and use the 1/2 diameter tool until the pencil disappears and repeat this process. This keeps the pressure off the outer edge, save the edge thickness and works faster.
![I.N "HALLUCINATION" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/n5B5q1Hwt_U/mqdefault.jpg)
![Seungmin "그렇게, 천천히, 우리(As we are)" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/kAzmhLHePqU/mqdefault.jpg)
Nice instructional video, Ed. Thanks for sharing. :)
You will need wheel 50 to 80 grit to keep it spherical and drive it concave, the brand is unimportant, just the grit size. Coarser diamond will work too and go faster but will take longer to clean up subsurface damage. However a 1/2 diameter wheel will remove some glass at the edge which you don't want if your blank is already thin or to save center thickness. So in my video I ran one or two smaller wheels 1/4 and 1/8 diam. for maybe 3 minutes to remove glass at the center. I then mark this area with a pencil and use the 1/2 diameter tool until the pencil disappears and repeat this process. This keeps the pressure off the outer edge, save the edge thickness and works faster.
These lens blanks are K-5 and came from United Lens. I saved them from being thrown away when 3M closed the Cincinnati plant.
Thanks. How do you know how many passes you need to do, in order to get to the desired curvature?
What is the name and type of that lapping/grinding equipment? Can one be purchased used affordably?